Digitally pulsed dielectric line scan recorder

ABSTRACT

A conductive paper web with a dielectric coating is fed over a writing roll where its surface receives image-defining electrostatic charges deposited by one of three pulsed line scan styluses bearing directly and successively upon it. The styluses are secured to an endless belt moving at constant velocity laterally of the web. The pulse stream for each line is accurately initiated as a function of stylus position and clocked from a rapid access storage by pulses mechanically synchronized with the belt drive. The latent image charged web is progressively festooned until a full sheet of video data is recorded, following which the web is severed and an image toning and fixing cycle is initiated to produce a hard copy.

United States Patent 1191 v Murray et al. 1 Sept. 4, 1973 s41 DlGlTALLY PULSED DIELECTRIC LINE 3,518,699 6/1910 Mitchell 346/74 ES 3,665,486 5/1912 Sato 346/74 as SCAN RECORDER 3,694,574 9/1912 Gray 6161. l78/6.6 A

Inventors: Richard D. Murray, Framingham;

Peter l Cone, Bedford; Allan B. Chertok, Cambridge, all of; David Shaler, Madison, NJ.

Assignee: EG&G, Inc., Bedford, Mass.

Filed: Jan. 6, 1972 Appi. No.: 215,872

Related US. Application Data [63] Continuation 6: Ser. No. 18,669, March 11, 1910,

abandoned.

[52] US. Cl. 346/74 ES {51] Int. Cl ..G03g 15/22 [58] Field of Search; 346/74 ES, 24;

[56] References Cited UNITED STATES PATENTS 3,644,930 2/1912 Stange 6: al 346/74 ES Primary Examiner-James W. Moffitt Attorney-Ralph L. Cadwallader et al.

[57] ABSTRACT A conductive paper web with a dielectric coating is fed over a writing roll where its surface receives imagedefining electrostatic charges deposited by one of three pulsed line scan styluses bearing directly and succes sively upon it. The styluses are secured to an endless belt moving at constant velocity laterally of the web.

The pulse stream for each line is accurately initiated as a function of stylus position and clocked from a rapid access storage by pulses mechanically synchronized with the belt drive. The latent image charged web is progressively festooned until a full sheet of video data is recorded, following which the web is severed and an image toningand fixing cycle is initiated to produce a hard copy.

19 Claims, 6 Drawing Figures PATENTED SHEET 1 UP 2 INVENTORS RICHARD D. MURRAY, PETER F. CONE, DAVID SHALER,ALLAN B. CHERTOK DIGITALLY PULSED DIELECTRIC LINE SCAN RECORDER This is a continuation of application Ser. No. 18,669 filed Mar. 11, 1970 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates generally to dry process facsimile recorders for producing a hard copy of graphic data supplied in electrical line scan format. The prior art includes facsimile receivers that have plural fixed point electrodes arranged in a transverse row across a web upon which image-defining electrostatic charges are deposited. An example is described in the US. Pat. to Schwertz No. 3,050,580 dated Aug. 21, 1962. These receivers are relatively complex and expensive and fail to provide graphic images having adequate resolution and other desired properties.

The U.S. Pat. to Clurman et al. No. 2,743,989 dated May 1, 1956, exemplifies another type of facsimile recorder having plural electrodes mounted serially on an endless belt moving laterally of the web. In these line scan recorders the web is a paper of an electrolytic type having a conductive base and surface. The mode of image formation results in hard copy of inferior quality, and there are other difficulties in operation including synchronization and speed control problems stemming from the particular means employed for controlling the variables.

In considering the merits of a facsimile recorder, attention must be given to the degree of simplicity or complexity in the structures employed and to various considerations entering into image quality. Further attention must be given in line scan recorders like Clurmans to problems of synchronization, since each of the electrodes (frequently called styluses) must be located at a margin of the writing surface for a particular line when the image producing electrical signal corresponds to the appropriate image information for that line at the corresponding margin of the image. The problems of synchronization include difficulties arising from the hitherto-assumed necessity for equal, precise spacing of the styluses along the periphery of the belt. Also, there have been substantial difficulties in the past resulting from the lack of synchronization between the belt speed and the rate of electrical graphic data transmission.

Features of hard copy quality that are desirable include sufficient contrast, gray scale capability, resolution, durability, stability of materials both prior to use and after deposit of the image on the web, image density and the extent of background pigmentation produced on areas of the image representing white. Prior art media include electrolytic, burnoff and carbon transfer techniques, all of which have certain disadvantages, some of which have been overcome in the more recent development of dielectric recording devices. However, these latter devices have not hitherto reached a state of development suitable for rapid printing facsimile applications wherein simple, low-cost recorders are adapted to produce hard copy of high quality within the meaning of the above criteria, and at adequate speeds for current and projected applications. Such applications include the transmission of weather maps by telephone lines or radio links, for a concrete example.

SUMMARY OF THE INVENTION This invention comprises a dielectric line scan recorder adapted for producing a hard copy upon an image forming medium consisting of an electrically conductive base paper coated with a dielectric material. The paper in web form is fed over a writing roll. While the web is in contact with this roll its surface receives image-defining electrostatic charges deposited by one of three pulsed styluses bearing successively upon it and secured to an endless belt moving at constant velocity laterally of the web. The charged web is progressively festooned while its leading end is held fast between feed rolls, until an end-of-map signal occurs representing the end of transmission of a full sheet of graphic data. Upon the arrival of this signal the web is severed, and the severed sheet is processed through a toning and fixing cycle. During development, triboelectrically-charged, pigmented plastic powder (referred to as toner) is deposited upon the charged surface, by means of a magnetic brush. The selectively deposited toner is then fixed by heat that fuses the plastic component permanently to the paper.

The image-defining electrical pulses are received from a rapid access storage clocked by pulses mechanically synchronized with the belt drive. In addition, photoelectric synchronizing means produce a signal upon the arrival of each stylus at a position in predetermined relation to the web margin, this signal being used to enable a circuit whereby the synchronized clock pulses are caused to deliver the graphic information from a serial memory containing a full line of data to be printed. By these means the necessity for equal spacing of the styluses on the belt is eliminated, and the graphic data are precisely deposited upon the web without the necessity for extremely high accuracy scan velocity control or precise synchronism with the transmitting scanner.

The foregoing and other features and details of the invention will be more clearly understood by reference to the following description of the preferred embodiment, having reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation in section illustrating the principal parts of the preferred embodiment.

FIG. 2 is a view in plan showing the principal parts of the scanning belt and styluses.

FIG. 3 is a side elevation showing a stylus assembly in operative relation to the web.

FIG. 4 is an elevation partially in section of the parts shown in FIG. 3, taken at right angles thereto.

FIG. 5 is a fragmentary exploded detail view showing parts of a sled employed in mounting a stylus assembly upon the belt.

FIG. 6 is a block diagram showing electrical controls for the recorder.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENT The hard copy medium employed in the practice of this invention preferably consists of an electrically conductive base paper coated with a dielectric material. The base paper is preferably a cellulose web containing conductive materials, for example polymeric quaternary ammonium salt and deliquescent salt or other comparable additives to increase conductivity. The diequivalent hard copy media may also be employed, in-

cluding thicker papers.

The mode of recording upon the hard copy medium includes scanning successive closely-spaced lines transversely of the web by means of styluses. A potential of several hundred volts is applied in pulses between a stylus and a backing platen roll through the thickness of the web. This leaves charges on the dielectric surface coating. As charges accumulate on the dielectric surface, opposite charges at the paper-dielectric interface flow through the conductive paper to or from the base electrode, and finally back to the stylus through the pulse circuitry and the printer frame. The accumulation of charges on the dielectric surface and the induced opposite charges at the dielectric-base paper interface create a strong field through the dielectric coatmg.

The latent electrostatic image so produced is converted into a visible image by the application and adherence of a triboelectrically-charged, pigmented, plastic powder or toner which has been previously charged oppositely to the charge on the dielectric surface. The charge upon the toner is produced by mixing it intimately with another material referred to as a carrier, for example spherical iron filings. This carrier when properly selected is not attracted to the latent electrostatic image during the application of the toner to the charged surface of the web. Fixing of the visible image is accomplished by heating the toner to the melting point of the plastic component which, upon cooling, solidifies and causes the toner to adhere to the dielectric surface.

FIG. 1 illustrates the principal parts of the preferred embodiment. A web 12 of hard copy medium or paper is fed from a supply roll 14 preferably housed in a thinwalled aluminum cassette (not shown) and passes from the latter through felt-lined lips. The cassette provides adequate protection for the paper against extreme ambient humidity or temperature conditions that would affect the paper handling and image forming characteristics adversely under certain conditions of operation.

The web passes over idler rolls l6 and 18 to a backing platen or writing roll 20 having suitable means (not shown) for accurate adjustment of its axis position. The roll 20 is preferably a steel roll grounded to the recorder frame, and is preferably driven in a precise manner by a stepping motor through a gear reduction, these elements being omitted from the drawing as they are of conventional form. The stepping motor preferably advances the web longitudinally in small steps, for example one mil (0.001 inch) per step. In the following description,-this and other exemplary or typical dimensional and speed data when stated are those for a particularrecorder built and successfully operated by the assignee of applicants, and such data are not to be construed as limiting the invention except to the degree inherent therein. This recorder was designed to print 18 inches X 36 inches weather maps transmitted by telephone lines or other modes of transmission, and as used herein the reference to map" denotes the entire stream of video data required to print a single sheet or map.

A steel or other conductive floating pinch roll 22 is urged by spring pressure toward the roll 20 to pinch the web, and bears against the dielectric coated side thereof. It is rubber covered on the edges outside the writing margins, the rubber being nearly flush with the steel intermediate surface, or very slightly raised above it for drive purposes.

A continuous belt 24 wrapped over pulleys 26 and 28 (FIG. 2) supports three spaced identical stylus assemblies 30, 32 and 34. A stylus 36 (FIG. 1) bears resiliently against the dielectric coated side of the web with a light spring pressure of about three to four grams. The belt is driven continuously at constant velocity by a motor 38 (FIG. 1) through a shaft 40 and the pulley 28, this motor having a pulse generator mechanically connected to it for sending out pulses on a line OP. The speed of the motor 38 is such that the stylus 36 travels the distance between a leading writing margin 42 and a trailing writing margin 44 in approximately onesixteenth of a second. In a typical machine for a web 19 inches width upon which the distance between the writing margins 42 and 44 is 18 inches, this means that the stylus travels at the rate of 288 inches per second. During a single scan the web preferably advances ten steps or a total of one-hundredth of an inch. At approximately the moment when the stylus assembly 32 reaches the trailing writing margin 44, the stylus assembly 30 arrives at the leading writing margin 42 in position to write the next succeeding line. Thus, the scanning pitch or resolution of the recorder in the described typical embodiment lengthwise of the web is onehundredth of an inch. However, for reasons that will be clear from the following description, it is not necessary that the assemblies 30, 32 and 34 be precisely spaced around the belt. To provide equal resolution lengthwise of the lines, means are provided to produce electrical image-defining impulses to the styluses at the rate of impulses per inch of stylus travel, or 1800 bits per line scan for the l8-inch writing width dimension previously described.

From the rolls 20 and 22 (FIG. 1) the web passes between guides 46 and 48 to a cutter comprising a rotatively reciprocal shearing blade 50 on a fixed axis and a flexed cutter blade 52 bearing on cylindrical edge portions of the blade 50. Upon actuation the blade 50 is reciprocated through a small angle to cut off the web transversely against the blade 52. Prior to this shearing action a length of the web is allowed to form a festoon 51 up to about 39 inches in length. Beyond the festoon the web passes between driven pinch rolls 53 and 54, with the previously sheared end of the web located on a line between a light source 56 and a photocell 58. The photocell 58 detects the arrival of the leading and trailing sheared ends of each sheet and functions in a sequence as follows.

An end of map signal reciprocates thev shearing blade 50 at a moment when a full map image is present within the section of the web comprising the festoon 51. The rolls 53 and 54 rotate at two different speeds. They are driven at a higher speed to feed the severed festoon rapidly into a toner or developer unit 60 and from the latter to a fixing unit 62 from which the hard copy sheet 64 emerges on a ramp 66 between two driven rolls 68. Details of the toner and fixing units are hereinafter further described.

While the severed sheet is being developed and fixed as it moves at the higher feed rate of the rolls 53 and 54 as described above, the leading edge of the web is free to pass over the blade 50, assuming that the next map is then being recorded by the styluses. Once the severed sheet has been removed into the developing and fixing units, a corresponding signal from the photocell 58 generated by the trailing edge causes a guide bar 70 to be pivoted about a support rod 72 into an alternate position 74, thereby causing the advancing edge of the web to be diverted into a path 76 leading directly to the rolls 53 and 54. When the web is seized by rolls 53 and 54, the rolls are rotating at a speed in excess of the speed at which the web is being metered out of the writing section rolls and 22 (FIG. 1). There is a slip clutch in the mechanical drive line to rolls 53 and 54 which allows these rolls to rotate more slowly as they are held back by the paper. In this mode the web is guided toward a position in the line between the light 56 and photocell 58. Upon the interruption of the light path to the photocell 58 by the leading edge of the web, the control 59 stops the rotation of the rolls 53 and 54 and rotates the rod 72 to swing the bar 70 to the position shown in full lines. As the new map continues to be recorded the web backs up into a new festoon 51, the length of the festoon depending upon the length of the new map. Preferably the end of map signal is a part of the data received in electrical form and is timed to occur when the recorded map has passed the position of the shearing blade 50.

STYLUS ASSEMBLIES Details of the structure of the stylus assemblies 30, 32 and 34, which are preferably identical, are shown in FIGS. 3, 4 and S. The body of the assembly consists of an insulating block 78 which may be formed of molded plastic, for example the thermoplastic acetal resin sold under the trademark Delrin by E. I. duPont de Nemours & Co. This block has an elongated longitudinal recess in which a helical compression spring 80 is received. The lower end of this spring as viewed in FIGS. 3 and 4 is received over a reduced end of a stylus spring screw 82 threaded into the block 78 and having a suitable socket head for making spring pressure adjustments. The other end of the spring rests on a metal cap 84 press fitted on the end of the stylus 36. The stylus is a pin slidable within a sapphire jewel mounting 86 fitted in a bore in the block 78 in line with the screw 82 and spring 80. The mounting 86 is preferably eccentric to permit alignment of all three styluses so that successive lines are equally spaced. The limit of movement of the stylus 36 in the direction toward the web 12 occurs when the cap 84 pushes the actuator 90 against the facing surface 88 of the block 78 at one end of the longitudinal recess in the latter.

Means are provided to depress the stylus 36 temporarily in the direction away from the web 12 as the stylus assembly 32 approaches and passes over the leading edge of the web. These means include a stylus actuator 90 formed of music wire. This actuator is pivotally retained by a U-shapedflat metal cap 92 fastened to a boss on the block 78 by a screw 94 and having slotted end portions (FIG. 4) between which a straight central portion of the actuator 90 is located. To facilitate proper location, a pair of brass disk washers 96 are soldered to the ends of this central portion. One of the ends of the actuator 90 extends into bearing contact with a surface of the cap 84, while the other end extends in the general direction of the web 12. A stop pin 98 is fitted into the block 78 in position to act as a stop for the actuator 90, defining a limit position for the latter in the direction corresponding to movement of the stylus away from the web 12.

A brush holder 100 is fastened by screws 102 threaded into the block 78, thereby clamping one or more wire brushes 104 formed to extend through an aperture 106 in the holder and normally resiliently bearing against one edge or bail portion defined by this aperture. The holder has an extension 108 resiliently bearing on the screw 82, whereby the brushes 104 are continuously in electrical connection with the stylus 36.

Referring to FIGS. 2 and 4, an insulating trolley bar 110 extends transversely of the web and contains a groove in which is received a metal strip 112, this strip being contacted by the brushes 104 and having electrical connection with a wire 114 connected with the electrical portion of the apparatus, further described below. In operation, electrical impulses of the desired amplitude and duration appear on the strip 1 l2 and are thereby connected through the brushes 104 with the stylus 36 then in operative relation to the web. No significant sparking occurs at the stylus. The amplitude of the applied voltage may be in the range of 200 to 600 volts D.C., the lower limit of this range corresponding to a lower limit of image density on the gray scale in the described machine having a stylus velocity of 288 inches per second, and the upper limit representing the higher limit of image density. It is found that potentials above 600 volts may produce a so-called bleeding effect," that is, the width of the developed line may increase above the width of the stylus as the voltage applied increases in the range above that potential. Thus, while a 10 mil stylus produces a 10 mil wide line when pulsed at 600 volts, it may produce a 25 mil wide line when pulsed at 1,000 volts. However, the bleeding effect may be reduced by reduction of the pulse width. Forexample, a pulse of 800 volts may be employed if the pulse width is reduced to 12 microseconds without adverse bleeding effects. Pulses of negative or positive polarity may be employed, although the positive polarity yields better definition in some cases, with some apparent loss of contrast.

Adjacent one side of the block 78 is a steel sled 116 having two square holes 1 18 (FIG. 5) and rounded end portions 120. Square-headed nuts 122 are secured to screws 124 and 126 passing through the block 78. By this means the block and sled are secured to square holes 128 punched in the belt 24, the latter having small curved edge cutouts such as 130 to prevent wrinkling when the nuts are tightened. The belt is preferably an endless woven Dacron belt impregnated with neoprene which has the desired resistance to stretching at the stylus velocity stated above when operated under the preferred tension of about ten pounds.

The pulleys 26 and 28 are crowned and at operating speeds the crowns alone are sufficient to hold the belt in proper position. The pulleys also have annular clearance grooves 132 to permit the passage of the nuts 122 as each stylus assembly passes around a pulley.

To prevent flutter of the stylus assembly as it traverses the web 12, magnetic retaining means are employed in association with the sled 116. Extending over the edges of the belt 24 (FIG. 4) are flat magnetic pole pieces 134 and 136 extending the full width of the web. These pole pieces have opposite polarities induced by a number of identical permanent magnets 138 (FIGS. 1 and 2) each of generally U-shaped configuration or otherwise formed and magnetized so that poles of like polarities are secured with filler pieces if desired to the same pole piece 134 or 136. The number and positions of these magnets can be varied as required to produce a stable path of movement of the stylus assembly from edge to edge of the web. The magnetic path is completed through the sled 1 16 which acts as a keeper and has its curved surfaces 120, which are preferably buffed to a polished finish, sliding upon the pole pieces 134 and 136 which act as rails, as shown in FIG. 4. The rails may be coated with a self-lubricating covering if desired.

As noted above, each stylus is depressed away from the web as it approaches and passes over the leading edge thereof, thereby preventing the stylus from tearing the web. This operation is performed by means of a synchronizing or framing detector assembly designated generally at 140 (FIGS. 2 and 4). Secured to this assembly is a cam or ramp 142 in position to engage an end of the stylus actuator 90 as the stylus assembly 32 approaches the paper edge, first lifting the stylus and then allowing it to settle into contact with the web after it has moved a short distance past the edge, under the pressure of the spring 80. Preferably, the axis of the roll 20 is accurately adjustable so that the stylus is depressed 0.015 to 0.020 inch when in writing contact with the web, in which position the stylus bears on the web with a pressure of 3 to 4 grams.

Also mounted in the assembly 140 are a pair of fiber optical members 144 and 146 which are opposed across a gap 148 aligned with the path of the styluses. At one end of the element 146 is a continuously illuminated light source 150, the element 144 being in turn connected with a photocell circuit whereby, upon the passage of a stylus through the gap 148, a very accurately determined pulse is generated on a lead SYNC for initiating the flow of graphic data to the writing stylus as further described below under the heading Operating Controls.

TONER AND FIXING UNITS The latent electrostatic image produced on the web must be maintained for the duration of the time interval between the start of the recording and the end of map" signal as previously described, at which time the toning and fixing operations are initiated. In the abovedescribed machine the maximum storage time may be over four minutes in the case of the leading edge of the web. As previously noted, the entire message is toned and fixed in a single brief continuous operation, which may be termed batch toning." This produces copy of uniform contrast as opposed to the varying contrast that might result if toner were applied continuously as the recording fixing proceed. Furthermore, the batch toning method is advantageous in that after actuation of the shearing blade 50, the severed sheet 64 can be delivered at a fast rate, well in excess of the feed rate at the writing plane, for delivery within seconds or less after the end of map" signal, without leaving a blank band of paper in the recorder.

Details of the toner 60 will be briefly summarized as various suitable toning techniques are available in the art, although some methods are preferable to others. In

ers. The corrugations prevent non-uniform toning that might result from a regular pattern.

The toner and iron filing carrier mixture is picked up by the magnetic roller from a trough. The roller brushes the charged paper over a contact region oneeighth to one-fourth inch wide, the excess mixture being removed by a doctor blade and allowed to fall back into the trough. Two auger screws (not shown) are used to circulate the toner and iron mixture to and from a reservoir. A toner replenisher (not shown) automatically adds pure toner to this reservoir to replace the toner consumed in the recording process.

Details of the fixing unit 62 are described as follows. The severed sheet 64 bearing toner is fed over a heat drum 154 heated to approximately 300 F by a heater 156. Fixing of the visible image is accomplished by heat passing through the backside (non-image side) of the coated paper. In the described machine, the fixing zone is about 6 inches so that any given area is heated no longer than one and one-half seconds during the fixing stage. One or more endless belts 158 passing over a plurality of rolls such as 160 are employed to carry paper over the drum 154 and into rolls 68. Suitable guides may also be employed to aid in producing good paperto-drum contact as well as to guide the paper into the exit rolls 68 and on out to a suitable stacking tray.

OPERATING CONTROLS The operation of the recorder will be further described by reference to FIG. 6 which shows a receiver 162 adapted to receive graphic information from the transmitter and retain it for delivery at the required rate to the styluses, as well as the end of map signal on a lead EOM. A suitable facsimile transmission system is described in a copending application of Charles G. Beaudette entitled Method and Apparatus for Producting a Compressed Digital Representation of a Visible Image, Ser. No. 5,642 filed Jan. 26, 1970, now abandoned, and assigned to the same Assignee as the present application. One of the inputs to the receiver is a lead CL extending from a conditioner circuit 164 which receives impulses on a lead OP extending from the pulse generator associated with the motor 38 (FIG. 1 This pulse generator produces pulses at a rate giving the required resolution along the recorded lines, which is 1,800 pulses per line scan in the above-described machine. The pulse generator may take any one of several forms but the preferred form is an electro-mechanical transducing system of the type described in US. Pat. No. 3,096,444 and which employs two discs having different numbers of equiangular sector which are alternately opaque and translucent, cooperating with a photoelectric transducer and light source, whereby pulses are produced in a sequence in exact synchronism with the movement of the belt 24. I

Another lead connected withthe receiver is a line ready" lead LR that extends to a flip-flop circuit 166. When the receiver is in a condition wherein an appropriate memory element thereof contains data corresponding to a complete line to be recorded, consisting in the above-described example of 1,800 bits, each bit corresponding to black or white, a signal appears on the lead LR to set the flip-flop 166. When the flipflop 166 is set a signal appears on a set output lead SO leading to an and gate 168. The other input to the gate 168 is the lead SYNC connected with a photocell impulse circuit 169 (FIG. 4) which produces an impulse upon the interruption of a light beam by each stylus as it reaches the gap 148 near the leading marginal edge of the paper web. The output of the circuit 168 is connected to a delay circuit 170 which introduces a delay equal to the time required for the stylus 36 to move from the gap 148 to the writing margin 42 (FIG. 2). The delayed impulse on a lead ENABLE resets the flip-flop 166. This same impulse also enables the receiver 162 to begin to clock out the graphic data for the stored line using the clocking pulses appearing on the lead CL, whereby a stream of graphic data pulses appears on the lead P and is applied to an amplifier 172 (FIG. 2). This amplifier elevates the pulses to the proper voltage level and applies them to the lead 114 through which they are connected to the stylus. It will be understood that the roll is grounded through the frame of the printer to provide a return circuit to the amplifier 172 for the writing pulses.

Several important advantages in operation will be recognized from the foregoing description. Since the pulses on the lead OP are derived directly from the movement of the belt drive to which the styluses are secured, it is ensured that the spatial interval between successive pulses will be constant along each line, even though the speed of the belt were to vary for any reason. This provides precise control over definition and ensures accurate reproduction of the transmitted graphic data.

A second important advantage derives partly from the fact that the receiver is adapted to store and hold each full line of data prior to the arrival of the stylus at the leading margin of that line. Also, the operation of the enabling and clocking circuits for the receiver determine the timing of the pulses on the lead P. By this means phase stability is ensured, that is, it is ensured that the first bit of graphic data for a line will produce the first recorded image bit on the web for that line, and each subsequent bit will be clocked out when the stylus is at the precise location corresponding thereto in said line. This method synchronization provides precise framing of the graphic data without the necessity of causing the writing stylus to reach the leading margin of each line at the same instant that corresponding data is being produced at the transmitter, as is necessary in many prior art facsimile systems.

In addition, it is not necessary for the stylus assemblies 30, 32 and 34 to be precisely equally spaced around the belt 24 to a tolerance less than a resolution element, as required in prior recorders. In the present recorder this spacing is not a factor in determining the precise point at which a line of printing is initiated. Unstead, each full scan line of video data is held in the receiver in readiness for printing and is clocked out after a predetermined delay interval fixed by the circuit 170, the start of this interval being determined by the arrival of the stylus in the gap 148.

It will be understood that while the invention has been described in detail with reference to a specific preferred exemplary embodiment, it is not limited either to its specific structure or to the magnitudes of parameters described above in relation thereto for purposes of illustration, except to the extent required by the appended claims.

What we claim is:

' 1. A dielectric recorder having, in combination,

a closed loop belt,

drive means for the belt including means to form a writing portion of the path thereof,

means to feed a sheet having a dielectric surface relatively to the belt in a direction transverse to said writing portion,

an electrically conductive support directly contacting the side of said sheet opposite to said dielectric surface along a dimension of the sheet spaced uniformly from said writing portion,

a plurality of stylus means secured to the belt in mutually spaced relationship, each adapted to bear independently and resiliently upon said dielectric surface opposite to said support while traversing the writing portion of said path,

means to apply electrical pulses between each stylus and said support at positions spaced along said writing portion to produce a latent image of a iine in the form of electrostatic charges on said surface,

means to apply an oppositely charged toner to said surface, and

means to fix said toner on the sheet to produce a hard copy of said image.

2. A recorder as defined in claim 1 in which the means to apply electrical pulses is synchronized with the drive means for the belt.

3. A recorder as defined in claim 1 in which each stylus means includes a body attached to the belt, astylus mounted on the body with provision for resiliently bearing on the sheet and an actuator operable to withdraw the stylus from contact with the sheet, and further including stationary ramps means adjacent an edge of the sheet to engage and operate the actuator of each stylus means to lift the stylus out of contact with the sheet as the stylus passes over the edge thereof and thereafter to allow the stylus to move into contact with the sheet.

4. A recorder as defined in claim 3 in which the last mentioned means include a cam.

5. A recorder as defined in claim 1 in which the means to apply electrical pulses include a digital memory for data representing said image and a pulse generator mechanically connected with the belt drive means and adapted to clock said data out of said memory to a stylus means.

6. A recorder as defined in claim 5 in which the digital memory has capacity for a full line of said image.

7. A recorder as defined in claim 1 in which the means to apply electrical pulses include a digital memory for data representing said image, a circuit having means enabling it to clock said data out of said memory to a stylus means, and synchronizing means in a predetermined position relative to said writing portion and cooperative with said stylus means to enable said circuit.

8. A recorder as defined in claim 7 in which said circuit clocks said data in synchronism with the drive means for the belt.

9. A recorder as defined in claim 8 in which the means to feed the sheet are adapted to advance it intermittently in discrete steps to space the line images produced by the stylus means in sequence.

10. A recorder as defined in claim 9 in which a plurality of steps occur during the production of the latent image for each line.

11. A recorder as defined in claim 1 in which each stylus means includes a body attached to the belt and a stylus mounted on the body with provision for positional adjustment thereon and for resiliently bearing on the sheet.

12. A recorder as defined in claim 11 in which the means to apply electrical pulses include a digital memory for data representing said image, a circuit having means enabling it to clock said data out of said memory to a stylus means, and synchronizing means in a predetermined position relative to said writing portion and directly operative by a stylus moving therethrough to enable said circuit.

13. A recorder as defined in claim 12 in which the synchronizing means include a light source, a photocell and means defining a light path from said source to said photocell, said path being interrupted by each stylus passing through said predetermined position.

14. A recorder as defined in claim 1 in which the means to feed the sheet include means to accumulate a length thereof during the period of production thereon of the latent images for a plurality of lines, and means to feed said length after said period continuously through the toner applying and fixing means.

15. A recorder as defined in claim 14 in which the sheet is fed at a first speed during said accumulation and at a higher speed through the toner and fixing means.

16. A recorder as defined in claim 14 further including means situated between said writing portion and the accumulated length of the sheet for severing the same.

17. A recorder as defined in claim 16 in which the sheet is in web form and is severed transversely of the web, said means to feed the sheet being adapted to arrest a severed end thereof between the accumulated length thereof and the toner applying means.

18. A recorder ,as defined in claim 17 in which said means to feed the sheet are operated by detecting the arrival of said severed end at a predetermined position to cause it to be arrested.

19. A recorder as defined in claim 17 in which said means to feed the sheet are operated by detecting the arrival of a leading severed end at a predetermined position to cause said end to be arrested and to cause the accumlating length to feed past said writing portion at a first speed, to be further operated upon actuation of the severing means to cause the accumlated length to feedthrough the toner and fixing means at a higher speed, and to be further operated by detecting the arrival of the trailing severed end at said predetermined position, to return to said first speed. 

1. A dielectric recorder having, in combination, a closed loop belt, drive means for the belt including means to form a writing portion of the path thereof, means to feed a sheet having a dielectric surface relatively to the belt in a direction transverse to said writing portion, an electrically conductive support directly contacting the side of said sheet opposite to said dielectric surface along a dimension of the sheet spaced uniformly from said writing portion, a plurality of stylus means secured to the belt in mutually spaced relationship, each adapted to bear independently and resiliently upon said dielectric surface opposite to said support while traversing the writing portion of said path, means to apply electrical pulses between each stylus and said support at positions spaced along said writing portion to produce a latent image of a line in the form of electrostatic charges on said surface, means to apply an oppositely charged toner to said surface, and means to fix said toner on the sheet to produce a hard copy of said image.
 2. A recorder as defined in claim 1 in which the means to apply electrical pulses is synchronized with the drive means for the belt.
 3. A recorder as defined in claim 1 in which each stylus means includes a body attached to the belt, a stylus mounted on the body with provision for resiliently bearing on the sheet and an actuator operable to withdraw the stylus from contact with the sheet, and further including stationary ramps means adjacent an edge of the sheet to engage and operate the actuator of each stylus means to lift the stylus out of contact with the sheet as the stylus passes over the edge thereof and thereafter to allow the stylus to move into contact with the sheet.
 4. A recorder as defined in claim 3 in which the last mentioned means include a cam.
 5. A recorder as defined in claim 1 in which the means to apply electrical pulses include a digital memory for data representing said image and a pulse generator mechanically connected with the belt drive means and adapted to clock said data out of said memory to a stylus means.
 6. A recorder as defined in claim 5 in which the digital memory has capacity for a full line of said image.
 7. A recorder as defined in claim 1 in which the means to apply electrical pulses include a digital memory for data representing said image, a circuit having means enabling it to clock said data out of said memory to a stylus means, and synchronizing means in a predetermined position relative to said writing portion and cooperative with said stylus means to enable said circuit.
 8. A recorder as defined in claim 7 in which said circuit clocks said data in synchronism with the drive means for the belt.
 9. A recorder as defined in claim 8 in which the means to feed the sheet are adapted to advance it intermittently in discrete steps to space the line images produced by the stylus means in sequence.
 10. A recorder as defined in claim 9 in which a plurality of steps occur during the production of the latent image for each line.
 11. A recorder as defined in claim 1 in which each stylus means includes a body attached to the belt and a stylus moUnted on the body with provision for positional adjustment thereon and for resiliently bearing on the sheet.
 12. A recorder as defined in claim 11 in which the means to apply electrical pulses include a digital memory for data representing said image, a circuit having means enabling it to clock said data out of said memory to a stylus means, and synchronizing means in a predetermined position relative to said writing portion and directly operative by a stylus moving therethrough to enable said circuit.
 13. A recorder as defined in claim 12 in which the synchronizing means include a light source, a photocell and means defining a light path from said source to said photocell, said path being interrupted by each stylus passing through said predetermined position.
 14. A recorder as defined in claim 1 in which the means to feed the sheet include means to accumulate a length thereof during the period of production thereon of the latent images for a plurality of lines, and means to feed said length after said period continuously through the toner applying and fixing means.
 15. A recorder as defined in claim 14 in which the sheet is fed at a first speed during said accumulation and at a higher speed through the toner and fixing means.
 16. A recorder as defined in claim 14 further including means situated between said writing portion and the accumulated length of the sheet for severing the same.
 17. A recorder as defined in claim 16 in which the sheet is in web form and is severed transversely of the web, said means to feed the sheet being adapted to arrest a severed end thereof between the accumulated length thereof and the toner applying means.
 18. A recorder as defined in claim 17 in which said means to feed the sheet are operated by detecting the arrival of said severed end at a predetermined position to cause it to be arrested.
 19. A recorder as defined in claim 17 in which said means to feed the sheet are operated by detecting the arrival of a leading severed end at a predetermined position to cause said end to be arrested and to cause the accumlating length to feed past said writing portion at a first speed, to be further operated upon actuation of the severing means to cause the accumlated length to feed through the toner and fixing means at a higher speed, and to be further operated by detecting the arrival of the trailing severed end at said predetermined position, to return to said first speed. 